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Torbay adopts i-Tree software that 'puts a value on trees'

Chris Baker

10th December, 2010

A new computer software package developed in the US puts a financial value on the ecosystem services trees perform, from reduced air pollution to the amount of carbon dioxide removed... can it now work in the UK?

Neil Coish's job is to make people love trees. And that is not always as easy as many of us would think.

Whether it's drifts of autumn leaves on cars, roads and pavements, or big trees that begin to block-out light, or interfere with a view, or that may or may not be about to topple over - the complaints come thick and fast.

Coish, senior tree officer at a large south coast local authority, is saddened by the trend for trees to be looked at as a source of hazard rather than wonder.

'We get so many enquiries about trees that are a problem, more enquiries about trees than litter on the street, and most of them are negative,' he said. 'It is amazing how many people see them as a nuisance rather than a benefit.'

Why is difficult to pin down, beyond yet more evidence of a society that recoils from the wild; or from risk, real and imagined.

To try to tilt the balance back towards trees, Coish is helping pilot a system to measure the benefits of what nowadays is termed the urban forest.

Forest survey

The i-Tree software, developed by the United States Forest Service, is designed to quantify the economic, environmental and social value of trees in towns and cities - in short put a dollar sign in front of them.

The project, at Torbay, in south Devon, is the first time i-Tree has been used in the UK and aims to adapt the software to British currency and conditions.

Coish said: 'What we are trying to do is get our trees on the local authority's general ledger, then they become assets. That is when we might start getting political support. They benefit us all, but we just take them for granted.'

Surveying all the borough's 28,000 trees, in manicured parks and gardens, orchards, hedgerows, surviving stands of gnarled ancient woodland, or clinging to the side of sea cliffs, would be impossible.

Instead, a small survey site was chosen at random in each of 250 squares drawn on a map, where everything was recorded: how many trees, their species, their size, the vegetation growing alongside, or whether the plot was entirely covered by bricks and concrete.

Computer says...

Once the information is fed into a computer i-Tree is able to quantify the urban forest's general characteristics, such as the total number of trees, what species they are and the density of the canopy.

It also calculates some of the nuts and bolts: how much pollution is being removed from the air, how much carbon stored or sequestered, much energy is saved because of shade in summer and slowed heat loss in winter.

As a pointer to how it works look at New York City, albeit about as far as it is possible to get from the fading charms of an English seaside resort.

When computers analysing the data spat out a value, the city was able to calculate that for every $1 spent on planting benefits accrued worth $5.6 - prompting a programme to plant a million more trees in the next ten years.

Air pollution absorbed by leaves saved an estimated $5 million a year; removing carbon dioxide from the atmosphere $755 million; reduced demand for electricity (by reducing cold winds in winter and adding shade in summer) $28 million; reducing storm water run off $36 million.

Jackie Lu, director of research and analysis at the city's parks department, said once the dollar numbers were known the argument in favour of valuing trees more became too compelling to ignore.

'That did have more resonance with the public, rather than saying "oh, they are so nice," or talking vaguely about the benefits of trees,' she said. So I definitely think it does help.'

The price of nature

Our own urban forest continues to be under-valued. Only five per cent of English local authorities have done any kind of cost benefit analysis, according to the government's recent Trees in Towns II report.

On average councils spend £1.38 per person per year on trees.

Yet trees are the most important part of the green infrastructure in towns and cities, according to Kenton Rogers, of Exeter-based forestry consultants Hi-Line, who was instrumental in bringing i-Tree across the Atlantic.

And (take a deep breath if you have an allergy to buzz-words) the eco-system services the urban forest provides, and i-Tree measures, will become increasingly important as climate changes.

Rogers heard about i-Tree at one conference, had a meeting of minds with Coish at another, and with the help of Forest Research - the research arm of the Forestry Commission - and Natural England the Torbay project was born.

He is only too familiar with the urban forester's dilemma: if you cannot measure the value of your trees how can you manage them? Precisely the problem Torbay's i-Tree project hopes to address.

Rogers said: 'If you don't put a value on something it is invisible to the bean counters. It is about making things visible to the people who only see pounds and pence.'

Community involvement

His one regret is the project, expected to cost about £30,000, did not receive enough funding to allow the community to help do the fieldwork - New York's successful strategy.

May be that will change if the Torbay experience is a success and other councils follow suit - the resort is, incidentally, a good test bed, with a larger than average variety of tree species and a representative cross section of urban and suburban development.

Even in these cash-straightened times local authorities such as Bristol, Luton, and the London boroughs of Camden and Islington, have already expressed an interest in using system.

Perhaps WH Auden's well-worn adage that a culture is no better than its woods should be applied to the urban forest too.

Most of us live in towns and cities, and may be the better society is the one that really does value its urban trees.

Results from the Torbay i-Tree project are expected in the spring.

Chris Baker is a freelance journalist

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